1. Field of the Invention
The present invention relates to a constant voltage generating apparatus with a simple overcurrent/short-circuit protection circuit.
2. Description of the Related Art
Generally, a first prior art constant voltage generating apparatus is constructed by an output transistor connected between an input terminal and an output terminal, and a voltage detection signal generating circuit serving as a constant voltage control circuit connected between the output terminal and a ground terminal to control the output transistor. For example, the voltage detection signal generating circuit is formed by a voltage divider connected between the output terminal and the ground terminal, and an error amplifier for receiving a divided voltage from the voltage divider and a reference voltage to generate a voltage detection signal for controlling the output transistor, so that an output voltage at the output terminal is brought close to a constant voltage defined by the reference voltage. This will be explained later in detail.
In the above-described first prior art constant voltage generating apparatus, however, if the output terminal is short-circuited via a load or the like to the ground terminal, an overcurrent may flow through the output transistor, so that the output transistor may be heated and destroyed.
In order to avoid such an overcurrent, a second prior art constant voltage generating apparatus is usually provided with an overcurrent/short-circuit protection circuit (see: JP-2002-169618 A) in addition to the elements of the first prior art constant voltage generating apparatus. This also will be explained later in detail.